The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a slider basecoat for reduced thermal pole-tip protrusion and recession.
Air bearing sliders have been extensively used in magnetic disc drives to appropriately position a transducing head above a rotating disc. In a disc drive, each transducer xe2x80x9cfliesxe2x80x9d just a few nanometers above a rotating disc surface. The transducer is mounted in a slider assembly having a contoured surface. An air bearing force is produced by pressurization of the air as it flows between the disc and slider and is a consequence of the slider contour and relative motion of the two surfaces. The air force prevents unintentional contact between the transducer and the disc. The air bearing also provides a very narrow clearance between the slider transducer and the rotating disc. This allows a high density of magnetic data to be transferred and reduces wear and damage.
Disc storage systems are designed for greater and greater storage capacities, the density of concentric data tracks on discs is increasing (that is, the size of data tracks and radial spacing between data tracks is decreasing), requiring that the air bearing gap between the transducer carried by the slider and the rotating disc be reduced. One aspect of achieving higher data storage densities in discs is operating the air bearing slider at ultra-low flying heights.
For the disc drive to function properly, the slider must maintain the proper fly height and provide adequate contact stiffness to assure that the slider does not contact the disc during operation. Also, the air bearing slider must have either enhanced take-off performance at start up or enhanced ramp load/unload performance to limit contact between the slider and the disc. Such contact would cause damage to the slider during take-off and landing of the slider.
Fly height is one of the most critical parameters of magnetic recording. As the average fly height of the slider decreases, the transducer achieves greater resolution between the individual data bit locations on the disc. Therefore, it is desirable to have the transducers fly as close to the disc as possible.
In a conventional air bearing slider, the slider body is formed from a substrate wafer of conductive ceramic material. On this substrate, a thin film of insulating material is deposited, and a metallic transducer is built therein, by a process such as sputtering. The transducer, which typically includes a writer portion for storing magnetically-encoded information on a magnetic media and a reader portion for retrieving the magnetically-encoded information from the magnetic media, is formed of multiple patterned layers successively stacked upon the substrate. The volume of the transducer is typically much smaller than the volume of the substrate.
The layers of the transducer, which include both metallic and insulating layers, all have different mechanical and chemical properties than the substrate. The differences in properties affect several aspects of the transducer. First, the layers of the transducer will be lapped at different rates. Thus, when an air bearing surface (ABS) of the transducer is lapped during its fabrication, differing amounts of the different materials will be removed, resulting in the transducer having an uneven ABS. Commonly, a greater amount of the metallic layers of the transducer will be removed during the lapping process than will be removed from the substrate. Thus, the lapping process results in a pole tip recession (PTR) of the metallic layers of the transducer with respect to the substrate. The PTR of a particular layer is defined as the distance between the planar air bearing surface of the substrate and the planar air bearing surface of that layer.
Additionally, the insulating material will often recede at an even greater rate than the transducer, leading to material recession that results in a discernable offset at the interface of the insulating material and the slider body substrate material. The variability of the offset prevents the transducer from flying as close to the surface of the magnetic disc as would otherwise be possible.
Further, the differing mechanical and chemical properties of the substrate and transducer layers further affect the air bearing surface during operation of the transducer. As the magnetic data storage and retrieval system is operated, the transducer is subjected to increasing temperatures within the magnetic data storage and retrieval system. In addition, a temperature of the transducer itself, or a part thereof, may be significantly higher than the temperature within the magnetic data storage and retrieval system due to heat dissipation caused by electrical currents in the transducer.
The coefficient of thermal expansion (CTE) is a measure of the change in length for a unit length of material for an incremental change in temperature. The CTE of materials used in forming the substrate is typically much smaller than the CTE of materials used in forming the metallic layers of the transducer. Due to the larger CTE of the transducer""s metallic layers, those layers tend to expand a greater amount than the substrate. Thus, when the transducer is subjected to higher operating temperatures, the metallic layers tend to protrude closer to the magnetic disc than the substrate; thereby affecting the PTR of the transducer. This change in PTR caused by temperature is referred to as the Thermal PTR (TPTR).
During operation of the magnetic data storage and retrieval system, the transducer is positioned in close proximity to the magnetic media. A distance between the transducer and the media is preferably small enough to allow for writing to and reading from a magnetic media having a large areal density, and great enough to prevent contact between the magnetic media and the transducer. Performance of the transducer depends primarily upon this distance.
To keep the distance between the transducer and the magnetic media constant, PTR should not change significantly with temperature. If TPTR is large, then the spacing between the transducer and the media will change significantly with temperature, thereby requiring the low-temperature fly height to be high enough to accommodate this variation at higher operating temperatures. On the other hand, if TPTR is close to zero, the low-temperature fly height can be reduced.
Thus, a need exists for an air bearing slider design which achieves a constant, ultra-low transducer flying height, despite the obstacles of differential mechanical and thermal recession. Much of the TPTR originates from the metal layers exposed at the air bearing surface. It is the mismatch in the CTE between the metallic layers of the transducer and the substrate material (which forms the air bearing surface), that gives rise to the thermal protrusion. An air bearing slider design is needed which eliminates the substrate from the air bearing surface and thereby reduces the TPTR of the transducing head.
The present invention relates to a magnetic head having an air bearing surface. The magnetic head includes a substrate having a disc opposing face bounded by a leading face, a trailing face, and first and second sided edges. The slider includes an end layer positioned upon the trailing face of the substrate wherein the basecoat has a disc opposing face and is comprised of a material having a coefficient of thermal expansion greater than a coefficient of thermal expansion of the substrate. An air bearing pad is formed solely on the disc opposing face of the end layer. A transducing head is formed in the air bearing pad and exposed at an air bearing surface.